Contiki 3.x
Data Structures | Macros
6LoWPAN implementation
The uIP TCP/IP stack

6lowpan is a Working Group in IETF which defines the use of IPv6 on IEEE 802.15.4 links. More...

Data Structures

struct  sicslowpan_addr_context
 The header for fragments. More...
 
struct  sicslowpan_nh_compressor
 The structure of a next header compressor. More...
 

Macros

#define DEBUG   DEBUG_NONE
 FOR HC-06 COMPLIANCE TODO: -Add compression options to UDP, currently only supports both ports compressed or both ports elided. More...
 
#define MAC_MAX_PAYLOAD   (127 - 2)
 Maximum available size for frame headers, link layer security-related overhead, as well as 6LoWPAN payload. More...
 
#define COMPRESSION_THRESHOLD   0
 Some MAC layers need a minimum payload, which is configurable through the SICSLOWPAN_CONF_MIN_MAC_PAYLOAD option. More...
 
#define sicslowpan_buf   uip_buf
 The buffer used for the 6lowpan processing is uip_buf. More...
 

Pointers in the packetbuf buffer

#define PACKETBUF_FRAG_PTR   (packetbuf_ptr)
 
#define PACKETBUF_FRAG_DISPATCH_SIZE   0 /* 16 bit */
 
#define PACKETBUF_FRAG_TAG   2 /* 16 bit */
 
#define PACKETBUF_FRAG_OFFSET   4 /* 8 bit */
 
#define PACKETBUF_IPHC_BUF   ((uint8_t *)(packetbuf_ptr + packetbuf_hdr_len))
 
#define PACKETBUF_HC1_PTR   (packetbuf_ptr + packetbuf_hdr_len)
 
#define PACKETBUF_HC1_DISPATCH   0 /* 8 bit */
 
#define PACKETBUF_HC1_ENCODING   1 /* 8 bit */
 
#define PACKETBUF_HC1_TTL   2 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_PTR   (packetbuf_ptr + packetbuf_hdr_len)
 
#define PACKETBUF_HC1_HC_UDP_DISPATCH   0 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_HC1_ENCODING   1 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_UDP_ENCODING   2 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_TTL   3 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_PORTS   4 /* 8 bit */
 
#define PACKETBUF_HC1_HC_UDP_CHKSUM   5 /* 16 bit */
 

Pointers in the sicslowpan and uip buffer

#define SICSLOWPAN_IP_BUF   ((struct uip_ip_hdr *)&sicslowpan_buf[UIP_LLH_LEN])
 
#define SICSLOWPAN_UDP_BUF   ((struct uip_udp_hdr *)&sicslowpan_buf[UIP_LLIPH_LEN])
 
#define UIP_IP_BUF   ((struct uip_ip_hdr *)&uip_buf[UIP_LLH_LEN])
 
#define UIP_UDP_BUF   ((struct uip_udp_hdr *)&uip_buf[UIP_LLIPH_LEN])
 
#define UIP_TCP_BUF   ((struct uip_tcp_hdr *)&uip_buf[UIP_LLIPH_LEN])
 
#define UIP_ICMP_BUF   ((struct uip_icmp_hdr *)&uip_buf[UIP_LLIPH_LEN])
 

HC06 specific variables

const uint8_t unc_llconf [] = {0x0f,0x28,0x22,0x20}
 
const uint8_t unc_ctxconf [] = {0x00,0x88,0x82,0x80}
 
const uint8_t unc_mxconf [] = {0x0f, 0x25, 0x23, 0x21}
 
const uint8_t llprefix [] = {0xfe, 0x80}
 

General sicslowpan defines

#define SICSLOWPAN_UDP_4_BIT_PORT_MIN   0xF0B0
 
#define SICSLOWPAN_UDP_4_BIT_PORT_MAX   0xF0BF /* F0B0 + 15 */
 
#define SICSLOWPAN_UDP_8_BIT_PORT_MIN   0xF000
 
#define SICSLOWPAN_UDP_8_BIT_PORT_MAX   0xF0FF /* F000 + 255 */
 

6lowpan compressions

#define SICSLOWPAN_COMPRESSION_IPV6   0
 
#define SICSLOWPAN_COMPRESSION_HC1   1
 
#define SICSLOWPAN_COMPRESSION_HC06   2
 

6lowpan dispatches

#define SICSLOWPAN_DISPATCH_IPV6   0x41 /* 01000001 = 65 */
 
#define SICSLOWPAN_DISPATCH_HC1   0x42 /* 01000010 = 66 */
 
#define SICSLOWPAN_DISPATCH_IPHC   0x60 /* 011xxxxx = ... */
 
#define SICSLOWPAN_DISPATCH_FRAG1   0xc0 /* 11000xxx */
 
#define SICSLOWPAN_DISPATCH_FRAGN   0xe0 /* 11100xxx */
 

HC1 encoding

#define SICSLOWPAN_HC1_NH_UDP   0x02
 
#define SICSLOWPAN_HC1_NH_TCP   0x06
 
#define SICSLOWPAN_HC1_NH_ICMP6   0x04
 

HC_UDP encoding (works together with HC1)

#define SICSLOWPAN_HC_UDP_ALL_C   0xE0
 

IPHC encoding

#define SICSLOWPAN_IPHC_FL_C   0x10
 
#define SICSLOWPAN_IPHC_TC_C   0x08
 
#define SICSLOWPAN_IPHC_NH_C   0x04
 
#define SICSLOWPAN_IPHC_TTL_1   0x01
 
#define SICSLOWPAN_IPHC_TTL_64   0x02
 
#define SICSLOWPAN_IPHC_TTL_255   0x03
 
#define SICSLOWPAN_IPHC_TTL_I   0x00
 
#define SICSLOWPAN_IPHC_CID   0x80
 
#define SICSLOWPAN_IPHC_SAC   0x40
 
#define SICSLOWPAN_IPHC_SAM_00   0x00
 
#define SICSLOWPAN_IPHC_SAM_01   0x10
 
#define SICSLOWPAN_IPHC_SAM_10   0x20
 
#define SICSLOWPAN_IPHC_SAM_11   0x30
 
#define SICSLOWPAN_IPHC_SAM_BIT   4
 
#define SICSLOWPAN_IPHC_M   0x08
 
#define SICSLOWPAN_IPHC_DAC   0x04
 
#define SICSLOWPAN_IPHC_DAM_00   0x00
 
#define SICSLOWPAN_IPHC_DAM_01   0x01
 
#define SICSLOWPAN_IPHC_DAM_10   0x02
 
#define SICSLOWPAN_IPHC_DAM_11   0x03
 
#define SICSLOWPAN_IPHC_DAM_BIT   0
 
#define SICSLOWPAN_IPHC_ADDR_CONTEXT_LL   0
 
#define SICSLOWPAN_IPHC_MCAST_RANGE   0xA0
 

LOWPAN_UDP encoding (works together with IPHC)

#define SICSLOWPAN_NHC_UDP_MASK   0xF8
 
#define SICSLOWPAN_NHC_UDP_ID   0xF0
 
#define SICSLOWPAN_NHC_UDP_CHECKSUMC   0x04
 
#define SICSLOWPAN_NHC_UDP_CHECKSUMI   0x00
 
#define SICSLOWPAN_NHC_UDP_CS_P_00   0xF0 /* all inline */
 
#define SICSLOWPAN_NHC_UDP_CS_P_01   0xF1 /* source 16bit inline, dest = 0xF0 + 8 bit inline */
 
#define SICSLOWPAN_NHC_UDP_CS_P_10   0xF2 /* source = 0xF0 + 8bit inline, dest = 16 bit inline */
 
#define SICSLOWPAN_NHC_UDP_CS_P_11   0xF3 /* source & dest = 0xF0B + 4bit inline */
 

The 6lowpan "headers" length

#define SICSLOWPAN_IPV6_HDR_LEN   1 /*one byte*/
 
#define SICSLOWPAN_HC1_HDR_LEN   3
 
#define SICSLOWPAN_HC1_HC_UDP_HDR_LEN   7
 
#define SICSLOWPAN_FRAG1_HDR_LEN   4
 
#define SICSLOWPAN_FRAGN_HDR_LEN   5
 

Address compressibility test functions

#define sicslowpan_is_iid_16_bit_compressable(a)
 check whether we can compress the IID in address 'a' to 16 bits. More...
 
#define sicslowpan_is_mcast_addr_decompressable(a)
 check whether the 9-bit group-id of the compressed multicast address is known. More...
 
#define sicslowpan_is_mcast_addr_compressable(a)
 check whether the 112-bit group-id of the multicast address is mappable to a 9-bit group-id It is true if the group is the all nodes or all routers group.
 
#define sicslowpan_is_mcast_addr_compressable48(a)
 
#define sicslowpan_is_mcast_addr_compressable32(a)
 
#define sicslowpan_is_mcast_addr_compressable8(a)
 

Detailed Description

6lowpan is a Working Group in IETF which defines the use of IPv6 on IEEE 802.15.4 links.

Our implementation is based on RFC4944 Transmission of IPv6 Packets over IEEE 802.15.4 Networks, draft-hui-6lowpan-interop-00 Interoperability Test for 6LoWPAN, and draft-hui-6lowpan-hc-01 Compression format for IPv6 datagrams in 6lowpan Networks.

Specifications implemented

Note
We currently only support 802.15.4 64-bit addresses.

RFC 4944

RFC4944 defines address configuration mechanisms based on 802.15.4 16-bit and 64-bit addresses, fragmentation of IPv6 packets below IP layer, IPv6 and UDP header compression, a mesh header to enable link-layer forwarding in a mesh under topology, and a broadcast header to enable broadcast in a mesh under topology.

We implement addressing, fragmentation, and header compression. We support the header compression scenarios defined in draft-hui-6lowpan-interop-00. This draft defines an interoperability scenario which was used between ArchRock and Sensinode implementations.

We do not implement mesh under related features, as we target route over techniques.

draft-hui-6lowpan-hc-01

draft-hui-6lowpan-hc-01 defines a stateful header compression mechanism which should soon deprecate the stateless header compression mechanism defined in RFC4944. It is much more powerfull and flexible, in particular it allows compression of some multicast addresses and of all global unicast addresses.

Implementation overview

6lowpan does not run as a separate process. It is called by the MAC process when a 6lowpan packet is received, and by the tcpip process when an IPv6 packet needs to be sent.

It is initialized from the MAC process, which calls sicslowpan_init (giving as argument a pointer to the mac_driver structure).

The main 6lowpan functions are implemented in the sicslowpan.h and sicslowpan.c files. They are used to format packets between the 802.15.4 and the IPv6 layers.

6lowpan also creates a few IPv6 and link-layer dependencies which are detailed in the next section.

Implementation details

Addressing

Link-layer addresses
The format of a 802.15.4 address is defined in uip.h.

/** \brief 64 bit 802.15.4 address */
struct uip_802154_shortaddr {
uint8_t addr[2];
};
/** \brief 16 bit 802.15.4 address */
struct uip_802154_longaddr {
uint8_t addr[8];
};
/** \brief 802.15.4 address */
typedef struct uip_802154_longaddr uip_lladdr_t;
#define UIP_802154_SHORTADDR_LEN 2
#define UIP_802154_LONGADDR_LEN 8
#define UIP_LLADDR_LEN UIP_802154_LONGADDR_LEN

Neighbor Discovery Link Layer Address options
The format of ND link-layer address options depends on the length of the link-layer addresses. 802.15.4 specificities regarding link-layer address options are implemented in uip-nd6.h.

#define UIP_ND6_OPT_SHORT_LLAO_LEN 8
#define UIP_ND6_OPT_LONG_LLAO_LEN 16
#define UIP_ND6_OPT_LLAO_LEN UIP_ND6_OPT_LONG_LLAO_LEN

Address Autoconfiguration
The address autoconfiguration mechanism also depends on the format of the link-layer address. The dependency is reflected in the #uip_netif_addr_autoconf_set function in #uip-netif.c.

#if (UIP_LLADDR_LEN == 8)
memcpy(ipaddr->u8 + 8, lladdr, UIP_LLADDR_LEN);
ipaddr->u8[8] ^= 0x02;

Packet Input/Output

At initialization, the #input function in sicslowpan.c is set as the function to be called by the MAC upon packet reception. The #output function is set as the tcpip_output function.
At packet reception, the link-layer copies the 802.15.4 payload in the rime buffer, and sets its length. It also stores the source and destination link-layer addresses as two rime addresses.

packetbuf_copyfrom(&rx_frame.payload, rx_frame.payload_length);
packetbuf_set_datalen(rx_frame.payload_length);
packetbuf_set_addr(PACKETBUF_ADDR_RECEIVER, (const rimeaddr_t *)&rx_frame.dest_addr);
packetbuf_set_addr(PACKETBUF_ADDR_SENDER, (const rimeaddr_t *)&rx_frame.src_addr);

It then calls the sicslowpan #input function. Similarly, when the IPv6 layer has a packet to send over the radio, it puts the packet in uip_buf, sets uip_len and calls the sicslowpan #output function.

Fragmentation

Note
Fragmentation support is enabled by setting the SICSLOWPAN_CONF_FRAG compilation option.
As we do not support complex buffer allocation mechanism, for now we define a new 1280 bytes buffer (sicslowpan_buf) to reassemble packets. At reception, once all the fragments are received, we copy the packet to #uip_buf, set uip_len, and call tcpip_input.
MAC_MAX_PAYLOAD defines the maximum payload length in a 802.15.4 frame. For now it is constant and equal to 102 bytes (the 802.15.4 frame can be maximum 127 bytes long, and the header 25 bytes long).

Header Compression

Compression schemes
The SICSLOWPAN_CONF_COMPRESSION compilation option defines the compression scheme supported. We support HC1, HC01, and IPv6 compression. HC1 and IPv6 compression are defined in RFC4944, HC01 in draft-hui-6lowpan-hc. What we call IPv6 compression means sending packets with no compression, and adding the IPv6 dispatch before the IPv6 header.
If at compile time IPv6 "compression" is chosen, packets sent will never be compressed, and compressed packets will not be processed at reception.
If at compile time either HC1 or HC01 are chosen, we will try to compress all fields at sending, and will accept packets compressed with the chosen scheme, as well as uncompressed packets.
Note that HC1 and HC01 supports are mutually exclusive. HC01 should soon deprecate HC1.

Compression related functions
When a packet is received, the #input function is called. Fragmentation issues are handled, then we check the dispatch byte: if it is IPv6, we treat the packet inline. If it is HC1 or HC01, the corresponding decompression function (#uncompress_hdr_hc1 or #uncompress_hdr_hc01) is called.
When a packet needs to be sent, we try to compress it. If only the IPv6 compression support is enabled, we just add the IPv6 dispatch before the 802.15.4 payload. If HC1 or HC01 support is enabled, we call the corresponding compression function (#compress_hdr_hc1 or #compress_hdr_hc01) to compress the packet as much as possible.

HC1 comments
In HC1, if the IPv6 flow label is not compressed, we would need to copy the fields after the flow label starting in the middle of a byte (the flow label is 20 bits long). To avoid this, we compress the packets only if all fields can be compressed. If we cannot, we use the IPv6 dispatch and send all headers fields inline. This behavior is the one defined in draft-hui-6lowpan-interop-00.
In the same way, if the packet is an UDP packet, we compress the UDP header only if all fields can be compressed.
Note that HC1 can only compress unicast link local addresses. For this reason, we recommend using HC01.

HC01 comments
HC01 uses address contexts to enable compression of global unicast addresses. All nodes must share context (namely the global prefixes in use) to compress and uncompress such addresses successfully. The context number is defined by 2 bits. Context 00 is reserved for the link local context. Other contexts have to be distributed within the LoWPAN dynamically, by means of ND extensions yet to be defined.
Until then, if you want to test global address compression, you need to configure the global contexts manually.

Macro Definition Documentation

#define COMPRESSION_THRESHOLD   0

Some MAC layers need a minimum payload, which is configurable through the SICSLOWPAN_CONF_MIN_MAC_PAYLOAD option.

Definition at line 176 of file sicslowpan.c.

#define DEBUG   DEBUG_NONE

FOR HC-06 COMPLIANCE TODO: -Add compression options to UDP, currently only supports both ports compressed or both ports elided.

-Verify TC/FL compression works

-Add stateless multicast option

Definition at line 76 of file sicslowpan.c.

#define MAC_MAX_PAYLOAD   (127 - 2)

Maximum available size for frame headers, link layer security-related overhead, as well as 6LoWPAN payload.

Definition at line 166 of file sicslowpan.c.

#define sicslowpan_buf   uip_buf

The buffer used for the 6lowpan processing is uip_buf.

We do not use any additional buffer.

Definition at line 260 of file sicslowpan.c.

#define sicslowpan_is_iid_16_bit_compressable (   a)
Value:
((((a)->u16[4]) == 0) && \
(((a)->u8[10]) == 0)&& \
(((a)->u8[11]) == 0xff)&& \
(((a)->u8[12]) == 0xfe)&& \
(((a)->u8[13]) == 0))

check whether we can compress the IID in address 'a' to 16 bits.

This is used for unicast addresses only, and is true if the address is on the format <PREFIX>::0000:00ff:fe00:XXXX NOTE: we currently assume 64-bits prefixes

Definition at line 240 of file sicslowpan.h.

#define sicslowpan_is_mcast_addr_decompressable (   a)
Value:
(((*a & 0x01) == 0) && \
((*(a + 1) == 0x01) || (*(a + 1) == 0x02)))

check whether the 9-bit group-id of the compressed multicast address is known.

It is true if the 9-bit group is the all nodes or all routers group.

Parameters
ais typed uint8_t *

Definition at line 254 of file sicslowpan.h.

Generated on Sun Nov 30 2014 09:59:06 for Contiki 3.x by   doxygen 1.8.5