switch(changes) {
	
	case 0:
		/*
		 * Nothing changed. If this packet contains data and the
		 * last one didn't, this is probably a data packet following
		 * an ack (normal on an interactive connection) and we send
		 * it compressed.  Otherwise it's probably a retransmit,
		 * retransmitted ack or window probe.  Send it uncompressed
		 * in case the other side missed the compressed version.
		 */
		if (ip->ip_len != cs->cs_ip.ip_len &&
			ntohs(cs->cs_ip.ip_len) == hlen)
		break;
	
	/* (fall through) */
	
	case SPECIAL_I:
	case SPECIAL_D:
		/*
		 * actual changes match one of our special case encodings --
		 * send packet uncompressed.
		 */
		goto uncompressed;
	
	case NEW_S|NEW_A:
		if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
			/* special case for echoed terminal traffic */
			changes = SPECIAL_I;
			cp = new_seq;
		}
		break;
	
	case NEW_S:
		if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
			/* special case for data xfer */
			changes = SPECIAL_D;
			cp = new_seq;
		}
		break;
	}
	
	deltaS = (u_short)(ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id));
	if (deltaS != 1) {
		ENCODEZ(deltaS);
		changes |= NEW_I;
	}
	if (th->th_flags & TCP_PSH)
	changes |= TCP_PUSH_BIT;
	/*
	 * Grab the cksum before we overwrite it below.  Then update our
	 * state with this packet's header.
	 */
	deltaA = ntohs(th->th_sum);
	BCOPY(ip, &cs->cs_ip, hlen);
	
	/*
	 * We want to use the original packet as our compressed packet.
	 * (cp - new_seq) is the number of bytes we need for compressed
	 * sequence numbers.  In addition we need one byte for the change
	 * mask, one for the connection id and two for the tcp checksum.
	 * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
	 * many bytes of the original packet to toss so subtract the two to
	 * get the new packet size.
	 */
	deltaS = (u_short)(cp - new_seq);
	if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
		comp->last_xmit = cs->cs_id;
		hlen -= deltaS + 4;
		pbuf_header(pb, -hlen);
		cp = (u_char *)pb->payload;
		*cp++ = changes | NEW_C;
		*cp++ = cs->cs_id;
	} else {
		hlen -= deltaS + 3;
		pbuf_header(pb, -hlen);
		cp = (u_char *)pb->payload;
		*cp++ = changes;
	}
	*cp++ = deltaA >> 8;
	*cp++ = deltaA;
	BCOPY(new_seq, cp, deltaS);
	INCR(vjs_compressed);
	return (TYPE_COMPRESSED_TCP);

	/*
	 * Update connection state cs & send uncompressed packet (that is,
	 * a regular ip/tcp packet but with the 'conversation id' we hope
	 * to use on future compressed packets in the protocol field).
	 */
uncompressed:
	BCOPY(ip, &cs->cs_ip, hlen);
	ip->ip_p = cs->cs_id;
	comp->last_xmit = cs->cs_id;
	return (TYPE_UNCOMPRESSED_TCP);
}

/*
 * Called when we may have missed a packet.
 */
void vj_uncompress_err(struct vjcompress *comp)
{
    comp->flags |= VJF_TOSS;
	INCR(vjs_errorin);
}

/*
 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
 * Return 0 on success, -1 on failure.
 */
int vj_uncompress_uncomp(
	struct pbuf *nb,
	struct vjcompress *comp
)
{
	register u_int hlen;
	register struct cstate *cs;
	register struct ip *ip;
	
	ip = (struct ip *)nb->payload;
	hlen = getip_hl(*ip) << 2;
	if (ip->ip_p >= MAX_SLOTS
			|| hlen + sizeof(struct tcphdr) > nb->len
			|| (hlen += getth_off(*((struct tcphdr *)&((char *)ip)[hlen])) << 2)
			    > nb->len
			|| hlen > MAX_HDR) {
		PPPDEBUG((LOG_INFO, "vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n", 
					ip->ip_p, hlen, nb->len));
		comp->flags |= VJF_TOSS;
		INCR(vjs_errorin);
		return -1;
	}
	cs = &comp->rstate[comp->last_recv = ip->ip_p];
	comp->flags &=~ VJF_TOSS;
	ip->ip_p = IPPROTO_TCP;
	BCOPY(ip, &cs->cs_ip, hlen);
	cs->cs_hlen = hlen;
	INCR(vjs_uncompressedin);
	return 0;
}

/*
 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
 * The packet is composed of a buffer chain and the first buffer
 * must contain an accurate chain length.
 * The first buffer must include the entire compressed TCP/IP header. 
 * This procedure replaces the compressed header with the uncompressed
 * header and returns the length of the VJ header.
 */
int vj_uncompress_tcp(
	struct pbuf **nb,
	struct vjcompress *comp
)
{
	u_char *cp;
	struct tcphdr *th;
	struct cstate *cs;
	u_short *bp;
	struct pbuf *n0 = *nb;
	u32_t tmp;
	u_int vjlen, hlen, changes;
	
	INCR(vjs_compressedin);
	cp = (u_char *)n0->payload;
	changes = *cp++;
	if (changes & NEW_C) {
		/* 
		 * Make sure the state index is in range, then grab the state.
		 * If we have a good state index, clear the 'discard' flag. 
		 */
		if (*cp >= MAX_SLOTS) {
			PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: bad cid=%d\n", *cp));
			goto bad;
		}
		
		comp->flags &=~ VJF_TOSS;
		comp->last_recv = *cp++;
	} else {
		/* 
		 * this packet has an implicit state index.  If we've
		 * had a line error since the last time we got an
		 * explicit state index, we have to toss the packet. 
		 */
		if (comp->flags & VJF_TOSS) {
			PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: tossing\n"));
			INCR(vjs_tossed);
			return (-1);
		}
	}
	cs = &comp->rstate[comp->last_recv];
	hlen = getip_hl(cs->cs_ip) << 2;
	th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
	th->th_sum = htons((*cp << 8) | cp[1]);
	cp += 2;
	if (changes & TCP_PUSH_BIT)
		th->th_flags |= TCP_PSH;
	else
		th->th_flags &=~ TCP_PSH;
	
	switch (changes & SPECIALS_MASK) {
	case SPECIAL_I:
		{
			register u32_t i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
			/* some compilers can't nest inline assembler.. */
			tmp = ntohl(th->th_ack) + i;
			th->th_ack = htonl(tmp);
			tmp = ntohl(th->th_seq) + i;
			th->th_seq = htonl(tmp);
		}
		break;
	
	case SPECIAL_D:
		/* some compilers can't nest inline assembler.. */
		tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
		th->th_seq = htonl(tmp);
		break;
	
	default:
		if (changes & NEW_U) {
			th->th_flags |= TCP_URG;
			DECODEU(th->th_urp);
		} else
			th->th_flags &=~ TCP_URG;
		if (changes & NEW_W)
			DECODES(th->th_win);
		if (changes & NEW_A)
			DECODEL(th->th_ack);
		if (changes & NEW_S)
			DECODEL(th->th_seq);
		break;
	}
	if (changes & NEW_I) {
		DECODES(cs->cs_ip.ip_id);
	} else {
		cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
		cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
	}
	
	/*
	 * At this point, cp points to the first byte of data in the
	 * packet.  Fill in the IP total length and update the IP
	 * header checksum.
	 */
	vjlen = (u_short)(cp - (u_char*)n0->payload);
	if (n0->len < vjlen) {
		/* 
		 * We must have dropped some characters (crc should detect
		 * this but the old slip framing won't) 
		 */
		PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: head buffer %d too short %d\n", 
				  n0->len, vjlen));
		goto bad;
	}
	
#if BYTE_ORDER == LITTLE_ENDIAN
	tmp = n0->tot_len - vjlen + cs->cs_hlen;
	cs->cs_ip.ip_len = htons(tmp);
#else
	cs->cs_ip.ip_len = htons(n0->tot_len - vjlen + cs->cs_hlen);
#endif
	
	/* recompute the ip header checksum */
	bp = (u_short *) &cs->cs_ip;
	cs->cs_ip.ip_sum = 0;
	for (tmp = 0; hlen > 0; hlen -= 2)
		tmp += *bp++;
	tmp = (tmp & 0xffff) + (tmp >> 16);
	tmp = (tmp & 0xffff) + (tmp >> 16);
	cs->cs_ip.ip_sum = (u_short)(~tmp);
	
	/* Remove the compressed header and prepend the uncompressed header. */
	pbuf_header(n0, -vjlen);

	if(pbuf_header(n0, cs->cs_hlen)) {
		struct pbuf *np;

		LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
		np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
		if(!np) {
			PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: prepend failed\n"));
			*nb = NULL;
			goto bad;
		}
		pbuf_chain(np, n0);
		n0 = np;
	}
	memcpy(n0->payload, &cs->cs_ip, cs->cs_hlen);

	*nb = n0;

	return vjlen;
	
bad:
	comp->flags |= VJF_TOSS;
	INCR(vjs_errorin);
	return (-1);
}

#endif


////////////////////////////////////////////////////////////////////////////////