Many popular point-to-point data link protocols use the high-level data lin
k control (HDLC) framing mechanism, which delineates protocol data units (P
DUs) by means of a special bit pattern or flag. When such a flag occurs in
the payload portion of a frame, an escape byte used to pad the transmitted
byte stream enables the receiver to differentiate between a true framing fl
ag and an occurrence of the flag pattern in the user information. The need
to process each byte in the incoming byte stream to identify the flag patte
rn makes this frame delineation method increasingly more complex and expens
ive to implement as the interface speed increases. In addition, the byte st
uffing operation performed when the flag pattern appears in the user inform
ation stream expands the carried traffic, interfering with quality of servi
ce (QoS) management procedures and making the link susceptible to malicious
attacks. These factors limit the scalability and QoS management capabiliti
es of the flag-based data link protocols, particularly at high link rates.
The increasing popularity of the packet over SONET (POS) protocol stack mak
es it desirable to find alternative framing protocols. In this paper, we pr
esent a simple data link (SDL) protocol. Based on using a Length Indicator
field and a header cyclic redundancy check (CRC) rather than a flag, to del
ineate frames, SDL is inherently scalable to high speeds and provides const
ant transmission overhead. We discuss the error control, delineation, and r
esynchronization mechanisms used by SDL, and we describe a link scrambler d
esigned to protect against malicious attacks that attempt to generate very
low bit transition density on the line. We also present additional link con
trol functions designed to make SDL suitable for next-generation multiservi
ce networks.