Link layer:services framing,link access: encapsulate datagram into frame,adding header,trailer channel access if shared medium "MAC"addresses in frame headers identify source,destination(different from IP address!) reliable delivery between adjacent nodes we already know how to do this! seldom used on low bit-error links wireless links:high error rates Q:why both link-level and end-end reliability? LinkLayer:6-6 Link layer: services ▪ framing, link access: • encapsulate datagram into frame, adding header, trailer • channel access if shared medium • “MAC” addresses in frame headers identify source, destination (different from IP address!) ▪ reliable delivery between adjacent nodes • we already know how to do this! • seldom used on low bit-error links • wireless links: high error rates • Q: why both link-level and end-end reliability? … … Link Layer: 6-6